The present application relates to a pattern-formed substrate having a fine pattern with a desired aspect ratio, particularly a fine pattern with a high aspect ratio. The present application also relates to a method of forming a fine pattern with a desired aspect ratio, particularly a fine pattern with a high aspect ratio (hereinafter, also simply referred to a pattern-forming method). The present application further relates to a die used for such a pattern-forming method.
In the past, fine patterns have been formed using lithography techniques and etching techniques. For example, a fine pattern is formed on a substrate as follows. First, a photoresist film is formed on a substrate. The photoresist film is exposed through a mask having a predetermined pattern arranged on the film and then developed to form a resist mask. Subsequently, the surface of the substrate is selectively etched through the resist mask, thereby forming the fine pattern on the substrate. The photoresists known in the art include organic resists and inorganic resists.
On the other hand, a wire grid device has been known as one of optical devices. The wire grid device is an optical device that functions as a polarization beam splitter or a polarizer in which gratings are formed on a glass substrate with a pitch of about 140 nm to 150 nm and a height of about 200 nm, or metal fine lines are periodically formed on the substrate. Fine patterns for gratings of the wire grid device are formed using the aforementioned lithography techniques and etching techniques.
For example, Japanese domestic re-publication of PCT international application (A1) No. WO 2004/04796 discloses a technology for patterning with an inorganic resist made of oxides of tungsten (W) and molybdenum (Mo) in a lithographic process for the formation of a fine pattern in the manufacture of a master for optical-disk production.
An inorganic resist is suitable for micro-fabrication as a photoresist material used in a lithographic technology, because of the formation of a pattern at a bit width almost corresponding to the half width of a light-focusing spot and obtaining a pattern width to be an almost half width by lowering an exposing power. On the other hand, an organic resist material is suitable for the formation of a deep-groove pattern but the minimum pattern width is almost the same as the wavelength of the exposure light. Thus, the organic resist material may not be suitable for the micro-fabrication in some cases.
In the case of the inorganic resist, the side wall of a pattern formed by exposure to the inorganic resist has an inclination of about 50°. Thus, it is difficult to form a structure with a desired depth when narrowing the space between the patterns. On the other hand, in the case of using a photoresist pattern as an etching mask, a deep pattern may be required for ensuring a selection ratio. Therefore, a technology for forming deep patterns while keeping the patterns at fine intervals has been demanded.